AFR Clarification

[Unchained]

You would have to weld the weep holes shut. At higher rpms with weep holes open (essentially an exhaust leak) the exhaust stream will suck in air (venturi effect) and add additional O2 to the exhaust stream. This will skew the O2 reading, causing a false lean reading.
In an EFI application, the ECM would respond to the lean O2 by adding unnecessary additional fuel.
Jay
Any air leaks would make the O2 sensor reading be incorrect.
The ECM would only add fuel if it was tied into the O2 sensor and set up in closed loop operation.
Closed loop would be the ideal but I've never been able to run that way because my Haltech E6Kwon't read a wide band O2 sensor.
I'm not really sure how many boat EFI systems run closed loop.
Ideally the fuel maps are set up so that in closed loop the ECM will only take away fuel and not add fuel. Closed loop only functions to about 70# throttle then you're running straight off the fuel maps anyways.

[ULTRA26 # 1]

Any air leaks would make the O2 sensor reading be incorrect.
The ECM would only add fuel if it was tied into the O2 sensor and set up in closed loop operation.
Closed loop would be the ideal but I've never been able to run that way because my Haltech E6Kwon't read a wide band O2 sensor.
I'm not really sure how many boat EFI systems run closed loop.
Ideally the fuel maps are set up so that in closed loop the ECM will only take away fuel and not add fuel. Closed loop only functions to about 70# throttle then you're running straight off the fuel maps anyways.
In a marine application at what RPM would you consider an AFR of 16:1 safe?
Thanks

[Unchained]

In a marine application at what RPM would you consider an AFR of 16:1 safe? Thanks
Maybe at idle or for very light loading but I always read that 14.7:1 AFR was stoichiometric and 12.5:1 was for max power.
Also I read that any mixture richer than 12:1 sutracted hp but some applications run a richer mixture to try to get some intercooling effect from the excess fuel.

[cfm]

In a marine application at what RPM would you consider an AFR of 16:1 safe?
Thanks
Okay, you're still digging for people to answer.
My answer is when loaded (getting on plane or faster)'Not in any gas marine engine I've had my hands on.' Decelration, idle, or shut off LOL is only time I'd be okay with it.
BTW: I'm referencing I/O applications. No jet or v-drive experience here.

[ULTRA26 # 1]

Maybe at idle or for very light loading but I always read that 14.7:1 AFR was stoichiometric and 12.5:1 was for max power.
Also I read that any mixture richer than 12:1 sutracted hp but some applications run a richer mixture to try to get some intercooling effect from the excess fuel.
Most guys that I have spoken with have stated that because Marine engines are always under a load (0 vacuum) 13:1 is a safe mixture throghout the powerband. I know that Merc Marine maps it's engines at 12.7:1 to 13:1 range.
Thanks

[Unchained]

I don't think you can assume that all marine engines are under a similar load.
0 vacuum is a pretty healthy load.
My TPR Stealth Jet boat at a 3000 rpm cruise speed had 10" of vacuum and stoich would be the proper AFR.
My V drive seems to be loaded more in relation to the cruise speed RPM and I believe the vacuum is around 5".

[Blown 472]

Yep, they would likely do that. I hadn't thought of it. Good call JAY.
But I am sure you have thought on how to tune the fuel curve for each cylinder so lets hear it.

[ULTRA26 # 1]

I don't think you can assume that all marine engines are under a similar load.
0 vacuum is a pretty healthy load.
My TPR Stealth Jet boat at a 3000 rpm cruise speed had 10" of vacuum and stoich would be the proper AFR.
My V drive seems to be loaded more in relation to the cruise speed RPM and I believe the vacuum is around 5".
10" of vacuum at 3000 rpm in a jet is amazing. 10" is almost like coasting. Didn't think that was possible.
Okay, you're still digging for people to answer.
My answer is when loaded (getting on plane or faster)'Not in any gas marine engine I've had my hands on.' Decelration, idle, or shut off LOL is only time I'd be okay with it.
BTW: I'm referencing I/O applications. No jet or v-drive experience here.
Per the response at the top, it sounds like Jets are under less of a load that I/O which is news to me.
Thanks for your input.

[Unchained]

10" of vacuum at 3000 rpm in a jet is amazing. 10" is almost like coasting. Didn't think that was possible.
Per the response at the top, it sounds like Jets are under less of a load that I/O which is news to me.
Thanks for your input.
For my setup there was a big engine in a small hull.
The opposite scenario would be a lot different load.
Checking manifold vacuum is real easy. Everyone should know what the cruising speed load is on the motor so they can tune to it. My engine spends most of its time at around 3000 rpm which gets me about 42 mph.
I'll copy a cruise speed datalog and put it up here later.

[ULTRA26 # 1]

For my setup there was a big engine in a small hull.
The opposite scenario would be a lot different load.
Checking manifold vacuum is real easy. Everyone should know what the cruising speed load is on the motor so they can tune to it. My engine spends most of its time at around 3000 rpm which gets me about 42 mph.
I'll copy a cruise speed datalog and put it up here later.
I don't hve a vacuum guage attached but my cruise is at about 3500 and about 52 mph. I've seen data sheets on a the same engine in a similar boat and Merc's AFR numbers at 3500 rpms were at 12.9:1. 496HO Stock Merc in a 26' cat.
Thanks look forward to seeing your logs